The present invention relates to a servo format and a data format for a magnetic disk and a magnetic disk device having a wide tracking servo band and high head positioning performance.
FIG. 4 shows an example of constitution of a magnetic disk device (HDD) 100. HDD 100 includes a head disk assembly (HDA) 200 including a magnetic disk 2, a magnetic head 1, a carriage 3, a read/write integrated circuit (R/W IC) 4 attached onto carriage 3, and a motor 5 and a package board (PCB) 300 including a read channel 31, a hard disk controller chip (HDC) 32, a servo control circuit (SC) 33, a microprocessor (MP) 34, a read-only memory (ROM) 36, and a random access memory (RAM) 37.
HDD 100 incorporated in a redundant arrays of independent disk (RAID) system or the like needs, in addition to a high-speed transfer rate and a large capacity, strength against external disturbance such as vibration for the following reasons. Many drives (HDDs) are disposed in a housing of the RAID system and operate at the same time and hence cause vibration stronger than that caused by operation of a single HDD. Therefore, to endure the environment, it is required to employ a positioning system which is strong again external disturbance of vibration.
FIG. 5 shows a layout of a servo area 27 and a data area 28 on magnetic disk 2. The areas are subdivided into a plurality of data zones 29 in a direction from an inner circumference to an outer circumference, and each zone has a data transfer rate. In this situation, to dispose a positioning system which is strong against external disturbance primarily of vibration, it is necessary to decrease the servo sample period and to improve the servo control band. A wide tracking servo band is guaranteed by increasing the number of servo sectors per disk circumference as shown in FIG. 12, which will be described later. FIG. 5 shows an example of construction in which the number of servo sectors is 32.
In a 3.5 inch HDD of 7200 rotations per minute (rpm) to 10000 rpm for the recent RAID system, the number of servo areas 27 can be increased and the servo sample period is reduced by minimizing the length of each servo area 27 per disk. In other words, this is because the physical length of the servo area can be reduced to about one half of the original length by changing the burst cycle frequency to a high value, i.e., from 20 MHz to 40 MHz as shown in FIG. 12, which will be described later.
This can be achieved primarily by a signal of a higher frequency (to be referred to as a servo frequency herebelow) for one bit of a servo signal (corresponding to one cycle of a signal in a position error signal (PES)). In the past several years, the servo frequency of the HDD for RAID has rapidly increased from about 10 MHz to a range from about 20 MHz to about 30 MHz, and the number of servo areas per circumference of a magnetic disk has increased from about 50/circumference to about 100/circumference. This has improved the servo band from about 400 Hz to about 800 Hz.
The total length of servo areas 27 in the circumferential direction little changes since the increase in the servo frequency is nearly of the same magnitude as that in the number of servo areas. Consequently, the ratio of allocation of data area 28 is kept unchanged. However, as shown in FIG. 6, as the number of servo areas increases, the chance in which a data sector is split (to be referred to as a split sector 25) in data area 28 becomes greater. This increases additional areas (shade areas in FIG. 6) such as AGC (automatic gain control (AGC)/phase locked loop (PLL) acquisition area) 17 of the data sector, and hence the data formatting efficiency is reduced.
FIG. 6 shows in its upper section a reproduced waveform 6 of a servo sector of a full format (the servo sector in this case is a zone corresponding to each servo area 27 drawn with a bold line in the radial direction in FIG. 5). Full-format servo sector 6 includes an AGC/PLL acquisition area (AGC/PLL) 7, a servo address mark area (AM) 8, a servo sector address area (SSA) 9-1, a track ID area (TID) 9-2, and position error signal areas (PESA to PESD) 10 to 13. This configuration includes PESA to PESD, for example, a signal of a fixed frequency is recorded at different positions in the tracking direction for A to D. Even two kinds thereof such as A and B can achieve the tracking control function.
These areas are arranged on magnetic disk 2 in its circumferential direction with an equal interval therebetween. The areas are discriminated from data to be demodulated according to a servo gate (SGATE) 14. Data sectors 25 and 26 are formatted in areas other than servo area 27. If the interval of SGATE 14 is sufficiently large, only a few data sectors are divided by a servo area at an intermediate point thereof as can be seen from a non-split sector 26, and hence no problem occurs. However, when the interval of SGATE 14 becomes smaller, the number of split sectors 25 divided by a servo area at an intermediate point thereof increases.
Non-split sector 26 includes fields of time (ISG1/2) 16 and 22 necessary for the rise and fall time of a read/write circuit system or the like and for absorption of fluctuation in rotation of magnetic disk 2, AGC 17 necessary to acquire AGC/PLL, SYNC 18 indicating a start point of data, encoded data (DATA), a cyclic check code (CRC) 23, an error correction code (ECC) 24, and PAD 21 necessary to determine data and to absorb a read delay of a read/write channel. However, since split sector 25 needs ISG1/2, AGC, SYNC, and PAD in duplication as indicated by shades, data area 28 is reduced.
One solution of this problem is to increase the servo frequency of servo area 27. Namely, by minimizing the physical length of the servo area, data area 28 itself is further enlarged. This idea is implemented in a method which, as disclosed in U.S. Pat. No. 5,784,219 (as shown in FIG. 7), employs a mixed configuration of servo sectors of full format 6 and short format 6-1. Short-format servo sector 6-1 is disposed between full-format servo sectors 6 to remove from short-format sector 6-1 the AGC/PLL, AM, SSA, and TID fields of the full format, namely, only PES is used. Since full-format servo sector 6 and short-format sector 6-1 appear alternately, the difference in format can be discriminated. The prior art shown in FIG. 7 as a configuration of the alternating arrangement of the full format and the short format of servo sectors. However, consideration has not been given at all to a relationship between this arrangement and the data split.
FIG. 10 shows a configuration example of servo sectors of the prior art. Full-format servo sector 6 of FIG. 6 includes AGC/PLL, AM, SSA, TID, and PESA to PESD respectively having lengths of 40, 8, 8, 16, and 12xc3x974 cycles, and hence the total length is 120 cycles as shown in FIG. 10. Short-format servo sector 6-1 includes PESA to PESD each having a length of 16.5xc3x974 cycles and the total length is 66 cycles. The PES length is elongated (from 12 cycles to 16.5 cycles) in consideration of fluctuation in the disk rotation and the like. The gain of AGC acquired in the preceding full format area is used for short format 6-1. Since synchronization of PLL is not required to demodulate PES of short format 6-1, AGC/PLL area 7 can be dispensed with.
By opening SGATE 14-1 for the short format using as a mark the AM position detected in the preceding full format area, SSA 9-1 and TID 9-2 can also be deleted for the short format 6-1. In this operation, only full-format servo sector 6 is decoded in the seek operation of the head, and short-format servo sector 6-1 is demodulated only in the following operation (in a state in which the head position is held at a predetermined track position). All of four PES information items of PESA to PESD of short format 6-1 are not necessary, and it is assumed that even two information items, i.e., PESA and PESB can cope with the operation in principle.
FIG. 11 shows formats of data sectors 25 and 26 in this case. Non-split sector 26 not split by a servo sector is 625 byte long, and split sector 25 split by a servo sector into a front field 25-1 and a back field 25-2 and has a total length of 690 bytes.
For the servo/data formats of FIGS. 10 and 11, the data area ratio (format efficiency) of a 10000 rpm HDD is calculated by changing the number of servo sectors and the burst cycle frequency (servo frequency). The data transfer rate is kept fixed as 30 MB/s. FIG. 12 shows results of the calculation.
The results of calculation of FIG. 12 are grounded as follows. Data sectors can be allocated to an area obtained by subtracting the servo area from an area corresponding to six milliseconds (msec) of one circumference. The number of non-split sectors can be calculated by subtracting the total split data sector length from the area. This leads to the total number of data sectors on the circumference of the magnetic disk. The data area ratio is calculated as a ratio of the area length determined by xe2x80x9c512-byte long user dataxc3x97total number of data sectorsxe2x80x9d to the length in the circumferential direction. The ratio of AGC or the like is calculated as a ratio of 65xc3x972=130 bytes for a split sector and 65 bytes for a non-split sector to the length in the circumferential direction. The ratio of ECC or the like is calculated as a ratio of xe2x80x9ctotal number of data sectorsxc3x9748 bytesxe2x80x9d to the length in the circumferential direction.
In FIG. 12, Type A is an HDD having a relatively narrow servo band in which the servo frequency is 20 MHz when the number of servo sectors is 80. It is assumed in this case that the number of split data sectors is 40 corresponding to about 50% of the number of servo sectors. Since the total number of data sectors is 260, the format efficiency (data area ratio) can be calculated as about 73.9%.
Type B1 is an HDD with an increased servo band with the servo area ratio kept unchanged. The number of servo sectors is increased to 160 and the servo frequency is increased to 40 MHz. Since the number of servo sectors is 160 and type A has 260 sectors, it is assumed that the number of split data sectors in this case is increased to 120 which is about 75% of the servo sectors. The increase in the split data sectors causes the area ratio of AGC or the like to be increased by 2.6 points from 10.8% to 13.4%. Therefore, the format efficiency (data area ratio) is decreased by 2.3 point to about 71.6%.
Type B2 shows a case of an application of U.S. Pat. No. 5,784,219 in which 50% of the 160 servo sectors of Type B are short-format servo sectors. Since the servo area ratio is improved by 1.8 points from 8% to 6.2%, the format efficiency is improved by about 1.5 points to about 73.1%. However, when compared with Type A of a narrow servo band (with a smaller number of servo sectors per disk circumference), the lowering of the format efficiency cannot be avoided.
As above, although a little improvement can be attained by combining short-format servo sectors of the prior art, the increase in the ratio of AGC or the like caused by the split data sectors is large as 2.6 points to 2.8 points. Therefore, it is unavoidable that the format efficiency is lowered by the increase in the servo band
To solve the problem above, the present invention primarily adopts constitution as follows.
In a magnetic disk including a plurality of servo sectors and data sectors which are divided along a circumferential direction, there are included servo sectors of a full format which are successively arranged in a radial direction of a magnetic disk and which include track information and servo sectors of a short format which are arranged between the full-format servo sectors, which are not successively arranged in a radial direction of the magnetic disk, and which include position error signals. The servo sector of the short format does not split a data sector.
In the magnetic disk, the short-format server sectors include a plurality of servo formats having different recording lengths.
The magnetic disk includes a gap of at least one track between data zones obtained by dividing an area of the magnetic disk from an inner circumference to an outer circumference thereof.
In a magnetic disk including a plurality of servo sectors and data sectors which are divided along a circumferential direction, a disk area is subdivided in a direction from an inner circumference to an outer circumference of the magnetic disk into a plurality of data zones each having one data transfer rate. There are disposed servo sectors of a full format which are successively arranged in a radial direction of a magnetic disk and which include track information and servo sectors of a short format which are arranged between the full-format servo sectors and which include position error signals. The servo sectors of the short format are not successively arranged in the radial direction between adjacent data zones.
In a magnetic disk device including a head disk assembly, a read/write channel, a hard disk controller, a servo control section, and a microprocessor, only full-format servo sectors which are successively arranged in a radial direction of the magnetic disk and which include track information are decoded during a seek operation and short-format servo sectors which are arranged between the full-format servo sectors, which are not successively arranged in a radial direction of the magnetic disk, and which include position error signals are demodulated during a following operation.
Full-format servo sectors which include track information are recorded to be successively arranged in a radial direction of a magnetic disk and short-format servo sectors including position error signals are recorded between the full-format servo sectors not to be successively arranged in a radial direction of the magnetic disk.
In a magnetic disk device including a head disk assembly, a read/write channel, a hard disk controller, a servo control section, and a microprocessor, there are included a signal processing circuit which decodes servo sectors of a full format which are successively arranged in a radial direction of a magnetic disk and which include track information which includes one input of a servo control signal indicating a servo sector. The signal processing circuit includes full-format sector detecting means for detecting from the full-format servo sector that the sector is a servo sector of full format and area creating means for constructing an area to detect from a result of the detection of the full-format servo sector a short-format servo sector including position error signals. A servo control signal inputted during an output operation of the area creating means is recognized as an indication of a short-format servo sector.